Ferdinand von Richthofen’s loess research in China

Abstract

Ferdinand von Richthofen (1833–1905), a great German geographer and geologist, was well known for his loess research in China. Here we reexamine the background of Richthofen’s loess research and review his contributions and limitations according to the existing literature. An important historical background of Richthofen’s loess research was that foreigners have been authorized to travel in the interior of China since the 1860s as a result of the Treaties of Tientsin. Richthofen made seven comprehensive scientific explorations in China in 1868–1872, whereas loess research was just one of his topics. He experienced dust weather on the Loess Plateau, where he had direct and deep impressions of the transport of dust, which should have helped him develop the hypothesis of the Aeolian origin of loess. Apart from the Aeolian hypothesis, his other achievements include the differentiation of the regenerated loess from the original loess, the discovery of the loess near Nanjing, the identification of the desiccated lakes as sources of dust storms, and the identification of “vertical cleavage” as a major property of loess.

Keywords

Richthofen loess Aeolian hypothesis Pumpelly China

I Introduction

Ferdinand von Richthofen, a prominent German geographer and geologist, was born on May 5, 1833 in Carlsruhe, Prussian Silesia, and died on October 6, 1905 (Daly, 1916). He was elected president of the Geographical Society of Berlin in 1873. From 1879 to 1983, he was a professor of geology at the University of Bonn. From 1883 to 1886, he was a professor of geology and physical geography at the University of Leipzig (Willis, 1905). He became a professor at the University of Berlin in 1886 and was the Rector of the University of Berlin, a position of honor conferred only upon the most distinguished scholars, from 1903 to 1904 (Willis, 1905).

He coined the term “Silk Road (Seidenstrasse)” (Richthofen, 1877). He significantly contributed to the research of geology and geography in China. The distinguished Chinese geologist W.H. Wong appraised that “geology of China is being built upon the solid foundation laid down by Ferdinand von Richthofen” (Wong, 1933).

A major contribution of Richthofen was his loess research in China. Loess was traditionally known as “Huang-tu (yellow soil)” in China, and Richthofen renamed it with the German origin scientific term “Loess.” He was the first to identify the Aeolian origin of loess.

Our knowledge of Richthofen’s loess research is not adequate apart from his Aeolian theory. What was the historical background of his loess research in China? In addition to Aeolian theory, what else did he contribute to the loess research? What are the limitations of his loess research? This research evaluates his loess research objectively and systematically in the field of physical geography based on the survey of the existing literature.

II Scientific and historical background of Richthofen’s loess research

The records of loess in Chinese historical literature can be traced back to over 2000 years ago. The earliest description of the loess was in a Chinese geographical document titled Tribute of Yu (Yu Kung or Yu Gong), which was composed approximately 2500 years ago. Both Richthofen and the US geologist R. Pumpelly (1837–1923) quoted Tribute of Yu many times in their loess researches (Pumpelly, 1866; Richthofen, 1907).

The classical Chinese literature recorded loess as “huang tu,” which means yellow soil. The modern academic term “loess” was coined by Karl Caesar von Leonhard in the early 19th century, and the first scientific research of the loess deposit was conducted by Charles Lyell in the 1830s (Lyell, 1834; Smalley et al., 2001). Lyell’s pioneering research was mainly based on the loess in the Valley of Rhine in Germany.

The loess deposits in north China are remarkable. They range up to several hundred meters in thickness, cover an area of nearly 440,000 km², and form the Loess Plateau (Liu et al., 1985; Figure 1).

Figure 1.

Map showing the distribution of loess in China (modified after An et al., 2014).

In 1866, Pumpelly described the Chinese loess scientifically for the first time (Pumpelly, 1918). In the 1860s–1880s, academia witnessed the earliest scientific research on the Chinese loess, including papers by Pumpelly (1866, 1877), Whitney (1877), Richthofen (1870, 1872, 1877, 1882), and Kingsmill (1871).

From a broad perspective of the historical background, the British defeated China in the first Opium War and forced China to sign the unequal Treaty of Nanking in 1842.¹ The British were no longer satisfied with the outcomes of the Treaty of Nanking a decade later and launched the Second Opium War together with the French in 1857. China was defeated again and forced to sign a series of unequal treaties (Treaties of Tientsin) with the western powers. Foreigners were then authorized to travel in the interior of China for tourism, trade, or missionary activities. British and French citizens were authorized to travel in interior China as a result of the Sino-British and Sino-French Treaties of Tientsin in 1858. Thus, British surveyor Thomas W. Kingsmill visited China in 1862 and commenced his loess research (Kingsmill, 1871). US citizens were also authorized to travel in interior China as a result of the Sino-American Treaty of Tientsin in 1858. When US geologist Pumpelly learned this news in the spring of 1863, he then decided to visit China and commence his geological explorations in China (Pumpelly, 1866, 1877).

Richthofen joined the Prussian diplomatic mission in 1860 under the leadership of Count Friedrich Zu Eulenburg to establish diplomatic and commercial relations with Siam (Thailand), China, and Japan. His rank was a legation secretary to Count Eulenburg, and his duty was to conduct geological studies (Anonymous, 1905; Daly, 1916; Wu, 2014). When the members of the mission returned to Berlin in 1862, Richthofen traveled to Shanghai to start his trips for research in China. Unfortunately, his plan could not be realized immediately. Until 1868, he made it to China and conducted seven geological and geographical explorations. He returned to Germany in 1872.

To be noticed, the reason for Richthofen’s failure to travel to China before 1868 was attributed to the social unrest caused by the Taiping Rebellion (1851–1864) in southern China (Jäkel, 2005). However, this cannot explain why Pumpelly and Kingsmill traveled in China in the early 1860s. We found another fact that would profoundly explain why Richthofen did not commence his explorations until 1868. China and Germany signed the Treaty of Tientsin in 1861, and German citizens were then authorized to travel in the interior of China. However, this treaty did not come into full effect until 1867.

Moreover, Richthofen had a discussion with Professor J.D. Whitney (Harvard University) in 1867. They reviewed the regions of the world where geological studies were most needed and concluded that China was the land which promised the richest results (Willis, 1905). This discussion encouraged Richthofen to devote to the geological research on China.

III Richthofen’s hypothesis of the Aeolian origin of loess

Richthofen made seven scientific explorations in China during 1868–1872, and observed the loess deposits carefully. He listed 12 evidences that support the Aeolian origin of loess, that is,

The petrographic, stratigraphic and faunistic difference of the loess from other deposits.

The nearly perfect homogeneity of composition and structure.

The independence of the distribution of the loess from the amount of altitude above sea level.

In hilly regions the loess, if little developed, fills up depressions between every pair of lower ridges, and in each of them presents a concave surface; but where it attains greater thickness, it spreads over the lower hills, and conceals the inequalities of the ground. Over table lands and plains, loess is spread in the shape of most uniform sheets.

The composition of pure loess is the same from whatever region specimens may be taken.

The almost exclusive occurrence of angular grains of quartz in the pure kinds of loess.

The complete absence of stratification.

The capillary structure caused by the occurrence of innumerable tubes, mostly encrusted with carbonate of lime.

The tendency to vertical cleavage.

The fact that land shells are imbedded in immense numbers throughout the loess. Freshwater shells are of extremely rare occurrence.

The great quantity of bones of mammals found in the loess.

The fact that wherever loess fills a basin between hills, their inclined slopes of are covered by angular fragments of the adjoining rock, on which the yellow soil rests.

In addition, we suggest that his experience of dust weather could have helped him develop the hypothesis of the Aeolian origin of loess. In his explorations, he experienced dust weather on the Loess Plateau and had direct and deep impressions of the transport of dust. He recorded that “Everything is yellow…Even the atmosphere is seldom free from a yellow haze, which is due to the diffusion through it of fine dust of loess” (Richthofen, 1872). “A fine yellow sediment of measurable thickness is deposited after every storm over large extents of country” (Richthofen, 1882).

It is very interesting that Richthofen’s first observation of the loess was near Nanjing in southeastern China in 1869. In his diary, he doubted Pumpelly’s fluvial origin hypothesis and Kingsmill’s marine origin hypothesis (Richthofen, 1907).

He rejected the opinions of freshwater or the marine origin of loess and preliminarily proposed the hypothesis of the Aeolian origin of loess in 1870 in Baron Richthofen’s Letters. The link between loess formation and the wind was worked out for the first time in a report titled “The Loess of Northern China,” which is Richthofen’s first essay that discusses the issue of Loess (Richthofen, 1870; Figure 2). The further introduction of the hypothesis was given in his monumental work “China” (Richthofen, 1877). Richthofen systematically elaborated his Aeolian hypothesis in the article titled “On the mode of origin of the loess” (Richthofen, 1882). The evidence supporting his hypothesis includes the independence of the distribution of the loess from the altitude and the nearly perfect homogeneousness of the composition and structure of the loess in different regions. Land shells are embedded in immense numbers throughout the loess, and the most delicate shells are perfectly preserved. However, freshwater shells are of extremely rare occurrence.

Figure 2.

“The Loess of Northern China” by Richthofen (1870).

Richthofen further noted that the transport of dust from the central Asia desert and Gobi regions to the Loess Plateau was related to the shifts of dry and wet seasons. However, he did not have the foresight to link it to the East Asian monsoon system, that is, the shift of humid summer monsoon and dry winter monsoon. Almost simultaneous to Richthofen’s research, New Zealand geologist John Hardcastle presented a paper entitled “On the Timaru loess as a climate register” (Hardcastle, 1890; Smalley et al., 2001) and demonstrated the relationship among climatic cooling/warming, glacier advancement/retreat, and loess formation on the Timaru plateau, New Zealand (Smalley, 1983). Decades later, Barbour (1931) tentatively linked the deposition of loess in China to the variability of summer and winter monsoons. A century later, Liu et al. identified the loess–paleosol sequence and discovered its relationship with the evolution of East Asian monsoon during the past 2.5 million years (An, 2000; Liu et al., 1985; Lu et al., 2004, 2010), which opens a new era of loess and global change research (Huang et al., 2000).

IV Influence of Richthofen’s Aeolian hypothesis

Pumpelly was the first geologist who studied the loess in China. He corroborated that the loess deposits were of lacustrine origin (Pumpelly, 1866). He conducted his field investigation in the river valleys to the northwest of Beijing Municipality, where many lakes lie, and his lacustrine hypothesis was based upon the sporadic loess deposits in this region. He would have had a different opinion if he has visited the Loess Plateau and witnessed the loess mantle ranging from hundreds of meters in thickness. After he learned Richthofen’s hypothesis of the Aeolian origin of loess, he was convinced by the following evidences: “There is one more peculiarity of the loess-it not only is wholly unstratified, but it contains the remains of only land animals, and especially of land snails” (Pumpelly, 1877). Pumpelly sincerely accepted it and confessed, “I am obliged to reject my own explanation of the origin of the Chinese deposits, and to believe with Richthofen that the true loess, where ever it occurs, is a sub-aerial deposit” (Pumpelly, 1877).

Whitney was among the earliest geologists who were fascinated by the Chinese loess. He accepted Richthofen’s Aeolian hypothesis in 1877. He stated that “A marine origin is rendered impossible by the absence of marine fossils, the constant presence of land shells and bones of land animals, as also by the absence of stratification and the very great differences of level at which the formation rests. The same arguments apply to the theory of a lacustrine origin” (Whitney, 1877).

G.F. Wright and F.B. Wright conducted a field investigation in northern China and the southern Siberia and added evidence for the Aeolian hypothesis. They found that the depths of loess deposits on the mountain slopes depended largely on the wind direction, instead of elevation (Wright, 1900, 1902). The comprehensive scientific exploration of the Loess Plateau from 1908 to 1909 by Clark also supported Richthofen’s Aeolian theory (Clark and Sowerby, 1912).

However, Kingsmill disagreed with Richthofen’s hypothesis and insisted on the marine origin of loess. Kingsmill was an English surveyor who arrived in Shanghai at the end of 1862 and remained there for the rest of his life. His geological surveys gave him a good knowledge of northern China, but he was wrong on this issue. He concluded that the loess was of marine origin because he believed that its underlying Mesozoic–Tertiary red sandstone formations were marine deposits, and the loess was formed in Tertiary. His false assumption was that within the Tertiary Period the whole of eastern Asia underwent a movement of depression and subsequent elevation. It is actually impossible that the Loess Plateau (800–3000 m a.s.l.) was below sea level during the Tertiary and Quaternary periods. He was fundamentally wrong because the red sandstones were actually terrestrial deposits, and the loess was actually quaternary deposits.

British consular officer Eric Teichman was another opponent of Richthofen’s Aeolian theory. He supported the fluvial origin of loess after a field trip that focused on the opium issue on the Loess Plateau (Teichman, 1921). He affirmed that the loess-like sediments in the fluvial plains of the Weihe River and the upper reaches of the Yellow River were of fluvial origin. He actually confused the fluvial origin regenerate loess with the Aeolian original loess.

After decades of debate (Ma, 1944; Zhang et al., 1987), the argument gradually settled and Aeolian theory was widely accepted by academia.

V Other achievements of Richthofen in loess research

1 Regenerated loess

Academia widely adopted that Russian geologist Obruchev first distinguished the difference between primary and secondary loess in the 1940s (i.e., redeposited and regenerated loess) (Obruchev, 1945; Pye, 1995).

However, Richthofen in fact had already differentiated the regenerated loess from the original loess. He worked out the term “regenerated loess” and demonstrated it as follows: “Loess carried away by water and re-deposited in basin. All fluvial plains in the loess regions are underlain by it, and where rivers are cut through the alluvial soil, they expose it to view. This formation is stratified.” Wright (1902) noticed the difference between the original and the regenerated loess and named it “modified loess.” Clark and Sowerby (1912) further differentiated the terms of “Huang-tu” and “loess.” “Huang-tu” refers to Aeolian or fluvial deposits, while loess refers to the pure Aeolian or sub-aerial deposits.

2 Loess near Nanjing

Richthofen’s other contribution to the loess science is his discovery of the so-called “Xiashu Loess” near Nanjing, which is a type of typical small-scale loess-like deposits in southeastern China (Figure 3). He stated, “They (hills) commence at the isolated, picturesque rock of Silver Island (Jiaoshan Island, Zhenjiang City) and extend forty miles west, but most of them are profoundly covered over by loess that they can only be detected by close examination…. A terrace of loess, from 80 to 200 feet in height, fringes and isolates them on all sides…. Opposite to these hills, on the northern bank of the Yangtze, the loess takes a predominant position” (Richthofen, 1871).

Figure 3.

Geological map of the Nanjing Mountains (currently known as Ningzhen Mountains) by Richthofen (1871). “L” denotes loess.

After the discovery of the Xiashu Loess, its origin has been the subject of intense debate over the past 100 years (Zheng et al., 2002).

3 Desiccated lakes: A source of dust

Richthofen and Pumpelly validated that deserts and desiccated lakes were the sources of dust (Pumpelly, 1877; Richthofen, 1882). Richthofen related that “The sediments of desiccated lakes, the soil which is laid bare by the retiring of the sea, the materials which are carried down by periodical torrents from glaciated regions to desert depressions, the particles which on every free surface of rock are loosened by constant decay—all these will be turned over again and again by the wind, and undergo an incessant sifting, until every earthy grain is blown off and nothing but moving sand and wind-worn pebbles remain” (Richthofen, 1882).

This significant dust source has been long neglected by many geologists, even the leading scientist on Chinese loess, like Liu Tungsheng. Until the early 21st century, the academics re-discovered that desiccated lakes were the major sources of dust storms in north China, Korea, and Japan (Abuduwaili et al., 2010; Goudie, 2009; Wang et al., 2004). Desiccated lakes significantly contribute to the fine particles of large-scale dust storms (Liu et al., 2015; Yao et al., 2008; Yue et al., 2004).

4 Vertical cleavage

Pumpelly noticed the “vertical cliffs” near Kalgan, currently known as the Zhangjiakou City of Hebei Province (Pumpelly, 1866). Richthofen first identified the “vertical cleavage” as the major property of loess (Figure 4). He claimed, “It is perfectly evident that no theory starting from the hypothesis of the deposition of loess by water can explain all or any single one of these properties,…the vertical cleavage…” (Richthofen, 1882).

Figure 4.

Vertical cleavage of loess (sketched by Richthofen, 1877).

VI Limitations of Richthofen’s loess research

1 Limitation of his explorations

Richthofen made a total of seven comprehensive scientific explorations in China from 1868 to 1872. He was a scientist with political agenda. A colonialist motivation was behind his explorations of the mineral resources and physical geography of China. He paid considerable attention to the mineral resources, particularly coal resources, and significantly helped for the German exploitation of the resources in the following decades (Wu, 2014). After explorations in Kiaochow (also known as Tsingtau and Qingdao), he advised the German government to occupy the Bay of Kiaochow as a naval base (Daly, 1916). Germany forced China to sign the unequal treaty “Convention for the Lease of Kiaochow” in 1898 and administered this area until 1914.

He carefully designed his scientific explorations, whereas loess research was just one of his topics. His routes of explorations indicate that he did not pay special attention to the Loess Plateau (Covering Shanxi, Shaanxi, and eastern Gansu Provinces;² Figure 5).

Figure 5.

Routes of Richthofen’s scientific explorations in China from 1868 to 1872 (Richthofen, 1877).

Some of the explorations were largely sponsored by the Shanghai Chamber of Commerce. He reported his results to them, which are now known as Baron Richthofen’s Letters (Hedin, 1933; Jäkel, 2005). Most of these letters are related with loess. However, only two letters contained specific reports on loess and are of key importance to loess research: “Letter from Baron von Richthofen on the Provinces of Honan and Shanxi” and “Letter from Baron von Richthofen on Chihli, Mongolia and Shanxi” (Richthofen, 1870, 1872). In the ‘Letter from Baron von Richthofen on Chihli, Mongolia and Shanxi,” Richthofen said, “I have devoted to the subject of the loess more space than may appear compatible with the scope and object of this letter” (Richthofen, 1872). Richthofen did not consider loess as a major topic of his explorations; otherwise, he would have gained even numerous achievements in the field of loess research.

2 Relationship among loess, paleosol, and soil

Another limitation of Richthofen’s loess research is that he considered the entire loess deposits as soil and failed to identify the paleosol formations in loess deposits.

He stated, “The loess is among the various substances which would commonly be called ‘loam’ because it is earthy and has a brownish yellow color. It is a productive soil…but owing to its property of being easily percolated by water, it needs more frequent and prolonged rains than most other kinds of soil” (Richthofen, 1870).

We now know that loess is a type of deposit and is composed of loess and paleosol layers, but Richthofen failed to identify the interbedding of loess and paleosol layers in the loess deposits. He related that “The soil is homogeneous from top to bottom, even in those instances where the vertical thickness is 1500 feet and more.” He even incorrectly suggested “the complete absence of stratification” as a character of loess (Richthofen, 1882).

He considered loess as soil given that he failed to identify paleosol layers. He failed to identify paleosol layers given that he considered loess as soil. No matter what was true for him at that time, Richthofen’s research is not completely correct in terms of his understanding on loess, which is a deposit rather than a soil.

Most of the scientists prior to the early 20th century have classified the entire loess deposits as a type of soil. Pumpelly and Whitney also considered loess as a type of soil. Pumpelly defined loess as a calcareous loam (Pumpelly, 1877).

Moyer was possibly the first scientist to consider loess in north China as a “parent material of soil” instead of “soil.” He affirmed that “Loess is by no means the only parent material of the soils of this region” (the loess region of North China) (Moyer, 1936).

Chinese pedologist Ma Rongzhi identified that loess was not soil but a type of soil parent material (Ma, 1944). Ma further discovered that the reddish-brown colored layers in the loess deposits were paleosol layers (Liu, 2008). In the 1980s, the chronology of loess with interbedded paleosols was established, and the shifts of loess and paleosol formations during the past 2.5 million years were identified as the indicators of environmental change (An, 2000; Kukla, 1987; Liu et al., 1985; Lu et al., 2004; Porter, 2001).

3 Is there loess in southwestern China?

Richthofen concluded that no loess existed in southwestern China. He claimed, “It (Tsinglingshan, now known as Qinling Mountain, southern Shaanxi Province) separates sharply the loess-region of the north from another to the south in which no loess occurs…. The Tsinglingshan (Qinling Mountain), which divides northern and southern Shensi (Shaanxi Province), is covered with loess on its northern slope. But that formation disappears completely on its southern side. Not a trace of it does exist in Szechwan (Sichuan Province)” (Richthofen, 1872).

Richthofen turned out to be wrong on this issue, and sporadic loess deposits were actually found on the south side of the Qinling Mountain (Gao et al., 2015; Lu et al., 2007; Sun et al., 2012, 2017; Zhang et al., 2009) and further south in Western Sichuan Province (Ou et al., 2012; Tian, 1966).

4 Calcareous concretions

Calcareous concretions are indicators of soil formation in arid and semi-arid environments. Kingsmill was the first person to identify the carbonate concretions and called them “beds of calcareous nodules” (Kingsmill, 1871). He validated that “the beds of calcareous nodules point to an apparent stratification of materials (loess)” (Kingsmill, 1871). Calcareous nodules are the by-products of soil-forming processes and are geologically not layers of the deposits.

Pumpelly noticed the carbonate concretions and recorded that “It (loess) is divided into beds varying in thickness from one foot to two or three hundred which thin out to nothing at the borders and are separated by parting planes” (Pumpelly, 1877).

Richthofen noticed the calcareous concretions. He recorded that “It contains, besides, carbonate of lime, the segregation of which gives origin to the well-known concretions common to all deposits of loess…” (Richthofen, 1882). However, he did not realize that the layers of calcareous concretions indicated soil (paleosol) formations in different geological times.

VII Conclusions

Richthofen’s achievements in the field of loess research were reviewed from the perspective of scientific history. As a result of the Treaties of Tientsin, foreigners have been authorized to travel in the interior of China since the 1860s, which commenced loess research in China. Richthofen proposed the hypothesis of the Aeolian origin of loess in Baron Richthofen’s Letters (Richthofen, 1870). The further introduction of the hypothesis was given in his monumental work “China” (Richthofen, 1877). Richthofen systematically elaborated his Aeolian hypothesis in the article titled “On the mode of origin of the loess” (Richthofen, 1882). His Aeolian hypothesis was accepted by many scientists in the late 19th century and early 20th century, except by Kingsmill and Teichman.

Apart from the Aeolian hypothesis, Richthofen’s other achievements include (a) his differentiation of the regenerated loess from original loess and his term “regenerated loess,” (b) his discovery of the “Xiashu Loess” near Nanjing, which is a type of typical small-scale loess-like deposits in southeastern China, (c) his suggestion that not only the deserts but also the desiccated lakes were the sources of dust storms, and (d) his identification of the “vertical cleavage” as a major property of loess.

Richthofen made seven comprehensive scientific explorations in China from 1868 to 1872. The colonialist motivation behind his explorations is evident. Loess research was just one of the topics.

The major limitations of Richthofen’s loess research include the following: (a) he concluded that no loess existed in southwestern China, but actually sporadic loess deposits exist on the south side of the Qinling Mountain and further south in Western Sichuan Province; (b) he considered the entire loess deposits as soil and failed to identify the paleosol formations in loess deposits and (c) he did not realize that the layers of calcareous concretions indicated soil (paleosol) formations in geological times.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by the Tin Ka Ping Education Fund (Hong Kong), Early Career Scheme project funded by the Research Grants Council of Hong Kong (Grant Number 28300717), and the German Academic Exchange Foundation (DAAD).

Notes

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